While gray car primer is a good primer, I have never had too much of a problem using Testor's white primer. However, what I have heard (and what your friend may have meant) is that it is best to spray gray primer FIRST, and then spray white primer if you absolutely have to have a white undercoat. The reason being that the gray primer is much finer and you can get a nice solid, smooth foundation. Also is you just spray white primer on the car, and say you paint the body gloss white, and the interior flat black, it may bleed through. With the solid gray primer on though, it will help keep the color bleed to a minimum.
Has anyone told you about Simple Green? It is completely safe on plastic, on your hands, etc, etc, and it will strip the paint off of a model without too much problem. It takes a little bit of time sometimes, but is much Safer than........Lacquer Thinner.
Make your friend sand the body...that aught to teach him!!! LOL